Yaneer Bar-Yam
Dustin D. Wind@yaneerbaryam For those who don't have money to drop on an expensive "official" device for air filtration, a Corsi-Rosenthal box can be a relatively-affordable godsend. Four furnace filters and a box fan, and it cleans air much faster than many "official" devices that cost 10x as much.
https://cleanaircrew.org/box-fan-filters/
DIY box fan filters – Corsi-Rosenthal box - Clean Air Crew
Also known as a Corsi-Rosenthal box, this DIY method of building your own air filter with MERV13 furnace filters and a box fan are an easy and cost-effective way to help clear indoor air from airborne virus particles, wildfire smoke, pollen, dust, and more! If you can seal a box, you can build one (or
@MySideIsHumanity I agree completely. Be aware that the relative filtration rates mean that at the time average level the Corsi-Rosenthal Box has to be 4X ACH to achieve the same level of filtration. So the 10X lower cost means that it is about 2.5X more cost effective.
David Elfstrom@yaneerbaryam @MySideIsHumanity The interesting thing about #CorsiRosenthalBox is that by using multiple filters the average face velocity of the filter is far below the ASHRAE 52.2 test condition.
It turns out that single pass efficiency of 0.3-1 micron is 80% at these low velocities, compared to the minimum 50% efficiency requirement for MERV-13.
@DavidElfstrom @MySideIsHumanity Great, that is about what I read. So for 80% that gives us a factor of 0.2 remaining after a filtering pass and .2^5 = 0.0003 that would put the 99.97% filtration at 5 filtering passes. Is that your point? I said 4X but it is about 5X?
If the rate was 0.5 then we would have to have about 8X.
@yaneerbaryam @MySideIsHumanity both in-room HEPA and a CR box, as well as outdoor air ventilation, act on mixed room air. All that's needed is the single pass efficiency to convert airflow to equivalent clean air rate. A CR box with 1000 m3/h airflow is approximately equivalent to a HEPA with 800 m3/h airflow. This is verified by test chamber particle removal.
@DavidElfstrom @MySideIsHumanity Happy to discuss and clarify. I will send you my phone number by DM.